The present invention relates generally to integrated circuit (IC) device fabrication and, more particularly, to a structure and method of forming electrically blown metal fuses for integrated circuits.
In integrated circuit devices such as complementary metal oxide semiconductor (CMOS) integrated circuits, it is often desirable to be able to permanently store information, or to form permanent connections of the integrated circuit after it is manufactured. Fuses or devices forming fusible links are frequently used for this purpose. Fuses can also be used to program redundant elements to replace identical defective elements, for example. Further, fuses can be used to store die identification or other such information, or to adjust the speed of a circuit by adjusting the resistance of the current path.
One type of fuse device is “programmed” or “blown” using a laser to open a link by exposure to high-energy light after a semiconductor device is processed and passivated, thereby (for example) activating a redundant circuit. This particular type of fuse device requires precise alignment of the laser on the fuse device to avoid destroying neighboring devices. This and other similar approaches can result in damage to the device passivation layer, and thus, lead to reliability concerns. For example, the process of blowing the fuse can cause a hole in the passivation layer when the fuse material is displaced.
Another type of fuse device is based on the rupture, agglomeration or electromigration of silicided polysilicon. These types of fuses include a silicide layer disposed on a polysilicon layer, and overlain by an insulating layer such as silicon nitride. The silicide layer has a first resistance and the polysilicon layer has a second resistance greater than the first resistance. In an intact condition, the fuse link has a resistance determined by the resistance of the silicide layer. In common applications, when a programming potential is applied, providing a requisite current and voltage across the fuse element over time, the silicide layer begins to randomly ball-up, eventually causing an electrical discontinuity or rupture in some part of the silicide layer. Thus, the fuse link has a resultant resistance determined by that of the polysilicon layer (i.e., the programmed fuse resistance is increased with respect to that of the first resistance). However, this type of fuse device can result in damage to surrounding structure and/or suffers from unreliable sensing because of the inconsistent nature of the rupture process and the relatively small change typically offered in the programmed resistance. Further, these types of devices may not be viable for use with many of the latest process technologies because of the required programming potentials (i.e., current flow and voltage levels over a requisite amount of time).
In still another type of fuse, namely an electromigration fuse, a potential is applied across the conductive fuse link via the cathode and anode in which the potential is of a magnitude and direction to initiate electromigration of silicide from a region of the semiconductor fuse reducing the conductivity of the fuse link. Electromigration is a term referring to the phenomenon of mass transport of metallic atoms (e.g., copper or aluminum) which make up the interconnect material, as a result of unidirectional or DC electrical current conduction therethrough. More specifically, the electron current collides with the metal ions, thereby pushing them in the direction of current travel. The electromigration is enhanced by commencing a temperature gradient between the fuse link and the cathode responsive to the applied potential. Even with an electromigration fuse, the programming of the fuse is still dominated by the polysilicon material. Since the polysilicon film contains a significant number of imperfections, the final resistance has a wide distribution. This sometime results in a programmed fuse from being sensed incorrectly, thus leading to the failure of the chip.
In summary, integrated circuit fuses are conventionally either laser blown by exposure to high-energy light or electrically blown with a high current introduced through the structure. Typically, when the fuse material is a metal, a laser is used to blow the fuse structure, and when the fuse material is polysilicon, a high current is used to electrically blow the fuse structure. Of the two programming mechanisms, an electrically blown fuse is generally preferred since the electrical signal can be applied to the wafer using the same wafer probers that are used to test individual chips. In other words, a laser blown fuse requires an additional tool set, as well as an increase in the time to test the wafers. On the other hand, a metal fuse structure is advantageous in that, among other aspects, they are flexible with respect to their location in the integrated circuit device. Another advantage of electrically blown fuses (with respect to laser blown fuses) is that the programming can be implemented in the field, in addition to during fabrication of the device.
Accordingly, it would be desirable to be able to provide a metal fuse structure that is electrically blown, and without the use of excessive voltages and currents for accomplishing the programming.